Tape drives may be used to receive user data from for example, computers and to store such data on tapes. The tapes may store a back-up copy of the user data, that will be required if the original has been lost or damaged. In such back-up applications it is of prime importance that the user data is retrievable. Therefore, there is an ongoing need to ensure that data storage devices such as tape drives and data-holding media such as tapes are as robust and secure as possible.
Once user data has been stored on the data-holding medium it can be held there for long periods. To recover the user data from the data-holding medium the data storage device must read the data-holding medium and regenerate the user data originally stored there. The data is normally split into discrete data items, each item including some user data and non-user data such as correction information, header information and information denoting the start and end of each data item The latter are called synchronisation fields or syncs. Sync detection is critical for reliable reading of the data from the data-holding medium. Various problems may occur in sync detection. For example, a sync may contain an error which results in it not being recognised, or spurious syncs may occur in the user data. To account for these, interpolation from a previously detected perfect sync has been used but this in itself has associated problems. It is an object of the present invention to provide a method and apparatus for improved sync detection.